This invention relates generally to electrical power transformation and more particularly, to a solid state circuit for performing the functions of a conventional iron core transformer.
Electrical power transformers are used primarily as voltage transformation devices. That is, the voltage input is either transformed up to a higher level, or down to a lower level. In the distribution of electrical energy, it is customary to transform the voltage up to a high level at the generating source, distribute the energy via transmission lines at the high level, then transform the voltage back down to a lower level for use by the load. This is the most efficient means of distribution over long distances. Over short distances, the transformer is used merely to adapt loads designed for different voltages to the local distribution system.
The power transformers consist of insulated copper wire wound on an iron core and in their simplest form consist of two windings usually referred to as the primary winding and the secondary winding. The turns ratio of these two windings establishes the voltage step up or step down capabilities of the device. At the very low power levels a single winding is sometimes used in a configuration referred to as an auto-transformer. In these devices, the input/output voltage ratio is varied by a sliding contactor, making electro-mechanical contact with noninsulated portions of the single winding.
The electrical power transformer has been the backbone of the electric utility distribution system for many years. The power transformer has a very high efficiency (98 percent) and a very good history of reliability. However, in these days of energy consciousness and environmental restrictions, all aspects of electrical hardware engineering from power generation, through distribution to the end use, are being subjected to question, even the trusted transformer.
There are applications of electrical power, especially in the military, where even the smallest of wave form defects/abnormalities cannot be tolerated, such as communication stations or data processing facilities. In addition, the Navy specifically has a problem in providing power to its piers because of the heavy loads represented by ships of all classes. Not only are these loads heavy but they are variable and intermittent, which poses a severe voltage regulation problem.
Any large user of electrical power such as the Navy will view even one-half percent increase in efficiency worthwhile because of the rising cost of electrical power. While 98 percent efficiency sounds extremely good, the two percent loss is a steady, constant loss, 24 hours of every day, which is primarily associated with the core losses of the transformer. This loss occurs whether the transformer is loaded or not. Therefore a better measure of cost effectiveness is not the classical efficiency of the transformer but one which includes a "use" factor which may be spread over the life of the installation.
Yet another problem is that the Navy has thousands of "askarel liquid" filled transformers, many of which are quite old. Askarel is formulated from polychlorinated biphenyl (PCB) and is now classified as a highly toxic, non-biodegradable pollutant under Title 40 Code of Federal Regulations. As of 1 Oct. 1977, the Environmental Protection Agency will no longer allow the sale of askarel filled transformers. Those transformers in the "field" must have the askarel removed and replaced by a substitute coolant in the near future. Unfortunately, the substitute liquids are more expensive and do not carry the same fireproof rating as askerel, which will result in yet higher costs for compensating external fire protection provisions in the installations. Even "dry-pack" type transformers are not the answer since they too are not considered fireproof by the National Fire Protection Agency and therefore cannot be used in certain locations. Indeed, an alternative to the conventional electrical power transformer as we know it today is desirable.